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Old 18-10-2010, 03:47 PM
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Terry B
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Join Date: Mar 2006
Location: Armidale
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Quote:
Originally Posted by alistairsam View Post
Hi
was looking for threads explaining Dec and RA gradations for EQ mount setting circles and found this thread.
I'm kind of getting my head around the Equatorial co-ordinate system and can understand how RA is divided into 24hrs, but can someone explain the How the Dec co-ordinates work.
I'm using an equatorial fork mount, and the RA axis is set to 38deg for Melbourne. That said, if I align my RA axis to point to the SCP, and the tube is parallel to the RA axis, my understanding is that the Dec is 90Deg. But I read that the Dec is divided into 4 quadrants of 90 deg.
So if I move my OTA on the Dec axis by 90 deg toward azimuth (alt/az) or overhead, would that be 0 deg Dec? what happens if I move further up?
to clarify, I'm starting Dec at 90 deg pointing to the SCP when RA is aligned to SCP, I then move only along Dec by 90 towards North, then Dec becomes 0, and how does the Dec axis increment or decrement? to -10deg, -20 deg and so on?

found this pic http://en.wikipedia.org/wiki/File:Se...rial_mount.jpg

secondly, in the eq co-ordinate system, if all objects have constand RA and Dec co-ordinates, what actually changes depending on time of day? is it the hour angle? I'm using stellarium to visualize.
Whe the scope is aimed at the SCP it is actually pointed at -90deg dec. As you point it away from the SCp towards the celestial equator you approach 0deg. If you go furter north you are then aiming into the +ve Dec area. the N celestial pole is+90 deg.
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